琼东南盆地陵水凹陷构造演化及其对深水大气田形成的控制作用

TECTONIC EVOLUTION AND ITS CONSTRAINTS ON THE FORMATION OF DEEPWATER GIANT GAS FIELD IN LINGSHUI SAG,QIONGDONGNAN BASIN

琼东南盆地陵水凹陷构造演化及其对深水大气田形成的控制作用成为深水区研究的热点。利用钻井地质、地震勘探资料,运用层序地层学、构造解析方法,认识了陵水凹陷的构造动力学机制和构造变形;探讨了陵水凹陷构造演化及其对深水大气田形成的控制作用;提出了陵水凹陷经历了古新世—始新世断陷、渐新世坳—断、早中新世断—坳和中中新世—更新世坳陷(深水盆地)4期构造演化阶段的新认识,并认为构造演化控制了深水大气田的形成。(1)古新世—始新世断陷、渐新世坳—断作用分别控制了湖相、海陆过渡相—海相烃源岩分布,中中新世—第四纪坳陷作用拓宽了烃源岩生气时窗;(2)渐新世坳—断作用控制发育了扇三角洲储层,中中新世—更新世坳陷作用控制发育了深水限制型、非限制型碎屑岩储层和碳酸盐岩生物礁储层;(3)渐新世坳—断演化阶段以走滑—伸展构造变形为主,控制发育了断鼻、断背斜圈闭,中中新世—更新世坳陷作用控制发育了深水限制型重力流水道砂岩性圈闭群、非限制型盆底扇岩性圈闭和生物礁地层圈闭;(4)渐新统、中中新统地层超压产生断裂/裂隙,构成了良好的天然气输导体系。

Recently, a deepwater giant gas field has been discovered in the Lingshui sag of the Qiong- dongnan basin. As the result, Cenozoic structures and their constraining effects on the formation of deepwater giant gas field has gained great attention from researchers. In this paper, well data and seismic data are applied to study the Cenozoic structural evolution of the sag and their controlling effects over the formation of deepwater giant gas field from viewpoints of sequence stratigraghy and structural analysis. Compared with previous studies, the coupling of structure evolution, tectonic mechanism, sedimentary infilling and natural gas accumulation are emphasized. It is revealed that the Cenozoic structure evolution of the sag consisted of stages of Paleocene-Eocene rifting, Oligocene de- pressing-rifting, Early Miocene rifting-depressing and Middle-Miocene to Quaternary depressing. Data suggests that. a. Oligocene depressing-rifting controlled the distribution of source rocks of marine- terrestrial transitional facies and marine facies, and the depression from Middle-Miocene to Quaternary expanded the gas generation window, b. Oligocene depressing-rifting provided the opportunity for the formation of fan-delta reservoir, and the depression from Middle-Miocene to Pliocene caused the forma- tion of confined and non-confined deepwater clastic reservoirs and reef carbonate reservoirs, c. Oligo- cene depressing-rifting later on provided the opportunities for the formation of various structural traps, such as the strike-slip-extention structures, fault-noses, fault-anticlines, and various litholog- ical traps such as deepwater confined channel sandstone of gravity flow, non-confined basinal litholog- ical traps and reef stratigraphic traps, d. overpressure in the stages of Oligocene depressing-rifting and Middle-Miocene depressing stages formed the new faults/fissures as the paths for migration.